The invention relates to a crankshaft drive of a V-type internal-combustion engine having a crankshaft with two mutually offset crank pins positioned between two crankshaft webs. A connecting rod is mounted on each crank pin by its large connecting rod eye. Each connecting rod is axially guided on a first side by a crankshaft web and on a second side, via an axial stop surface arranged on the rod shank-sided part of the large connecting rod eye, by a non-lateral-load-bearing intermediate web which interconnects the two crank pins, a projected contour of intermediate enveloping that of the two crank pins.
In the case of the crankshaft drive disclosed by German Published Unexamined Application (DOS) No. 3,541,903, the radii intersections and associated high notch stresses, which are problematical from aspects of production engineering, are avoided by the use of an intermediate web between the offset crank pins.
In the case of the crankshaft drive disclosed by German Published Unexamined Application (DOS) No. 3,541,903, the radii intersections and associated high notch stresses, which are problematical from aspects of production engineering, are avoided by the use of an intermediate web between the offset crank pins.
An object of the present invention is to provide a crankshaft drive of the type described above which both minimizes the required amount of machining on the intermediate web and ensures an optimum axial guidance of the two connecting rods at each position of the crankshaft during rotation of the crankshaft.
This object is achieved according to preferred embodiments of the invention by providing the intermediate web with an axial stop collar on either side and with an enlarged cross-sectional area so that at each crankshaft position, the projected cross-sectional area of the intermediate web extends over the axial stop surface of a respective connecting rod.
The design of the crankshaft drive according to the invention advantageously ensures that the axial stop surface arranged on the connecting rod facing part of each large connecting rod eye does not jut out beyond the projected contour of the intermediate web during crankshaft rotation, so that the connecting rod eyes always abut the intermediate web over a maximum stop surface. Furthermore, with the crankshaft drive constructed according to certain preferred embodiments, the fine machining of the intermediate web is restricted to just a surface grinding of the two axial stop collars according to the invention.
The crankshaft drive according to the invention makes possible the general use of connecting rods having bearing covers which are not involved in the axial guidance of the connecting rods. An increase in the mass of the crankshaft drive due to the intermediate web can thus be compensated for by a reduction in width of the bearing cover. Preferably, the width of respective bearing covers for the connecting rod connections with the crankshaft is reduced by an amount corresponding to the increase in weight resulting from the addition of the intermediate web.
In order to achieve an improvement in the load bearing capacity of the connecting rod bearings in certain preferred embodiments, the bearings are widened in the direction of the intermediate web. This is made possible due to the provision of designing the crank pin transition radii facing the intermediate web smaller than crank pin transition radii facing the crankshaft web. This arrangement corresponds to the distribution of stresses along the throw arrangement, in which, due to the form factors, the maximum stresses occur in the region of the basic pin flutes.
Further, the load bearing safety of the crankshaft is improved in the region close to the intermediate web by subjecting the smaller, and consequently more notch-sensitive transition radii facing the intermediate web, to a peripheral radii hardening of a relatively low hardness depth penetration. This hardening is executed so that the resulting hardening zones on either side of the intermediate web do not intersect and leave a soft zone at the overlapping cross-section of the crank pins. The low hardness penetration depths of the crank pin transition radii facing the intermediate web, due to the small width of the intermediate web, compared with the basic web radii, provides that an even transition of the hardness profile along the pin length is appropriate.
An additional safeguard against peripheral hardening cracks in the intermediate web at the transition from the hardened to the unhardened regions can be achieved according to certain preferred embodiments by dimensioning the hardness penetration depth in the intermediate web transition such that a narrow unhardened zone remains on a level with the imaginary radii intersections.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.